BAGHDAD, Iraq, March 17 — Heider Abbas stumbled through the rubble, calling out: "Shovels! Shovels! We need shovels!"
He had seen charred bodies. He had lifted heavy stones. He had heard cries for help.
"There is a family under all this," said Mr. Abbas, a 24-year-old car washer, to no one in particular. "Help me. Please."
Fires crackled around him. The streets were thick with panicked people. Men in bloody clothes hauled out injured and dead people — on stretchers or in their arms.
These were the chaotic first moments after a large explosion rocked Karada, an upscale neighborhood in Baghdad, on Wednesday night, bringing down an apartment building, shearing off the facade of a hotel and killing at least 27 people.
At first it was not clear what caused the blast, which made windows across the city quiver. American officials later said it was a huge car bomb. Some Iraqis had said they thought it was a rocket attack.
The ambulances that rushed to the scene were quickly overcome by masses of distraught people.
"Don't bring us the dead people!" the drivers yelled over loudspeakers. "We can't help them. Bring us the injured."
American soldiers arrived minutes later. They jumped out of their Humvees in bulletproof vests and tightly laced combat boots. They cordoned off the streets and pushed the crowd back.
"Move! Move! Move!" they shouted. When some Iraqis resisted, the soldiers pointed their guns in people's faces. "We're not kidding. Get out of here."
Old women shook gray little fists. Young men stuck out their chins and yelled back.
"Why are you blocking us from rescuing our people?" asked Faiz Sadeh, a construction worker.
A half hour after the explosion, two fire engines showed up. Firefighters tugged a hose through the dark, smoky streets. All street lamps were out. Everything was lighted by flames. The Mount Lebanon Hotel, home to many foreign workers, was burning, along with a nearby apartment building, several cars, oil drums, trees and even laundry flapping on clotheslines.
"Why do they attack here?" asked Essat Al Said, a carpenter. "There is nothing important here."
Conspiracy theories began to circulate. A missile. An American bomb. An errant helicopter strike. Two empty ambulances that tried to drive away were quickly mobbed by an angry crowd.
"You can't leave now!" men shouted. "There are children buried inside."
The ambulance drivers were surrounded. They turned back toward the fires. The focus of attention was a crater gouged in front of the hotel, 10 feet deep and 20 feet across.
The explosion happened at 8:15 p.m., when Karada's sidewalks were alive with men selling juice, families strolling and chickens roasting on the spit.
Mr. Abbas said he had been at a neighborhood cafe when he saw the blue flash and heard the big boom. He dashed into the burning buildings and reached for anything that moved.
"I carried three people who were badly hurt," he said, as he looked up at the burning hotel. "There were many other people screaming for help. I saw some bodies that were completely black."
Mr. Abbas shook his soot-streaked face. A moment later, he headed back in.